Behavior and mechanism of the adsorption/desorption of tectonically deformed coals

The physical and chemical texture of tectonically deformed coals produced by various formational mechanisms are different from those of primary coals, thus resulting in major differences among the physical properties of the reservoirs of these coals. We have studied the adsorption/desorption behavior of tectonically deformed coals by the use of isothermal adsorption/desorption experiments under equilibrium moisture condition. Experiments of isothermal adsorption/desorption of methane or multi-component gases have indicated that, the adsorption curves of coals with a low degree of tectonic deformation conform to the type of isothermal adsorption curve described by the Langmuir equation; the methane adsorption curves of coals with strong tectonic deformation cannot be described by the Langmuir equation. The adsorption/desorption process of methane and multi-component gases in the deformed coals is not consistent with primary coals, which form an effect of hysteresis in different kinds of tectonically deformed coals. With the change of pore structure of tectonically deformed coals at reservoir condition, the added adsorbed CH₄ in the experiments is desorbed on the pore surface of coals during the pressure reduction process. Thus, the result shows that the adsorption volume in the process of desorbing is greater than that in adsorbing. Because of the deformation, structural change, and transformation of the adsorption potential field of coals, it is essential to form a new kind of isothermal adsorption curve and the hysteresis effect of the desorption process. Supported by National Basic Research Program of China (Grant Nos. 2006CB202201 and 2009CB219601) and National Natural Science Foundation of China (Grant Nos. 40772135, 40642013 and 40172058)     

不同变质变形煤特征对煤层气富集渗流的制约

煤岩是煤层气的主要储集层,其变质变形作用对煤层气的赋存、运移和开发都具有重要意义。本文以华北地区典型含煤区为研究区,基于现场资料分析、煤岩显微观测,孔渗测试及压汞实验分析,探讨了不同变质变形煤储层孔渗特征,并从裂隙、孔隙不同尺度探讨了不同变质变形煤储层特征及其孔、裂隙结构特征对煤层气富集渗流所起的作用。结果表明,首先,煤层气产出过程与煤储层变质变形特征密切相关;实验室测定的渗透率与试井渗透率具有可比性,一般碎斑煤大于碎裂煤;高变质弱变形煤储层和中变质弱变形煤储层煤层气的富气能力与渗流能力比较强,是煤层气富集高渗的有利储层。     

构造煤的测井曲线判识-以柿庄北区块为例

为定量判识构造煤并获取其分布信息,以测井曲线技术为指导研究了构造煤的地球物理特征。总结了煤体结构测井参数变化规律并做出了测井曲线模版,并应用此原理对柿庄北区块煤体结构进行了研究。结果显示:构造煤具有自然伽马负异常、声波时差正异常、低电阻率、井径扩径、人工伽马高幅值等特征;人工伽马与声波时差组合对于煤体结构划分具有较好的判识性。柿庄北区块15号煤构造煤(46%)比3号煤更为发育(13%),为制约15号煤煤层气产量的关键因素;柿庄北区块东北部与西南部构造煤发育,主要受西部NE-NNE向断层及褶皱的控制。     

Relationship between nanoscale deformation of coal structure and metamorphic-deformed environments

The relation between coal structure (including molecu-lar and pore structures) and metamorphism has been dis-cussed over a century. It has seldom involved nano-scale structure deformation of coals and its metamorphism- de-formed environment, especially the factor of stress influ-ence on nano-scale structural deformation. Instead the influence of temperature and pressure on the coal structure has been the primary focus. As a result, part studies indi-cated that temperature is the main factor th…     

Thermal simulation of the formation and evolution of coalbed gas

Thermal simulation experiment of gas generation from the peat and the coals were performed using the high temperature and pressure apparatus, at temperature ranging from 336.8-600℃, a pressure of 50MPa and two heating rates of 20℃/h and 2℃/h, and the evolution and formation of coalbed gas components were studied. Results show that for the coals, the gaseous products are mainly composed of hydrocarbon gases. However, for the peat the content of hydrocarbon gases in gaseous products is lower than that of non-hydrocarbon components. In the generated hydrocarbon gases methane is predominant and heavy hydrocarbon gases (C2-5) are present in small amount. Meanwhile, carbon dioxide (CO2) predominates the generated non-hydrocarbon gases, and hydrogen (H2) and sul-furated hydrogen (H2S) are existent in trace amount. It is also observed that temperature is the main factor controlling the evolution of coalbed gas generation. With increasing vitrinite reflectance, methane rapidly increases, CO2 sightly increases, and C2-5 hydrocarbons first increase and then decrease. The peat and Shanxi formation coal have a higher generative potential of coalbed gases than coals and Taiyuan formation coal, respectively, reflecting the effect of the property of organic matter on the characteristics of coalbed gas component generation. In this study, it is found that low heating rate is favorable for the generation of methane, H2 and CO2, and the decomposition of C2-5 hydrocarbons. This shows that heating time plays an important controlling role in the generation and evolution of coalbed gases. The results obtained from the simulation experiment in the study of coalbed gases in natural system are also discussed.     

流固耦合作用下注气开采煤层气增产规律研究

提高低渗透煤层气产量是我国煤层气开采中急需解决的关键问题,加速煤层甲烷解吸过程的注气增产方法是提高低渗透煤层气产量的有效途径。由于排采降压在孔隙流体压力变化的范围内会引起储层孔隙介质的应力和应变的变化,造成有效渗透率和孔隙度的降低,同时也影响注气和产气的动态参数。研究这些规律,首先建立了注气开采煤层气多组分流体扩散渗流的流固耦合模型,利用数值方法研究了注气开采煤层气的增产机理。研究表明,注入二氧化碳气体不但减少了煤层甲烷的分压．加速了煤层甲烷的解吸;而且二氧化碳气体比甲烷气体更易吸附,竞争吸附置换煤层甲烷分子,从而提高了煤层气产量,同时必须重视耦合作用对注气增产造成的不利影响。     

关键层—应力墙瓦斯突出机理

认为瓦斯突出的发生和发展受控于赋存在岩石－含瓦斯煤－岩石体系中诸多因素的综合作用,并在此基础上提出了关键层－应力墙的瓦斯突出机理。     

褐煤储层含气量计算

因我国褐煤中煤层气赋存特征认知程度较低,影响了较低煤级煤层气的开发,褐煤中含气量的研究显得尤为关键。基于此,文中对采自内蒙古海拉尔盆地4个褐煤H1,H2,H3,H4样品进行煤岩煤质分析,25℃平衡水等温吸附实验。计算埋深在400～2 000 m吸附气含量;模拟在储层温度、压力、矿化度、密度条件进行甲烷溶解度的测定结果表明甲烷溶解度随压力、温度的同时增加而增大(低于80℃),基于实验结果,计算了不同埋深(温度、压力)下褐煤储层的水溶气含量;测定4个褐煤样品孔隙度,根据马略特定律计算游离气含量。由吸附气、水溶气及游离气含量计算褐煤含气量。结果表明,埋深小于1 000 m的褐煤含气量随埋深增加而增大;埋深大于1 000m随埋深增加而减少。H1含气量较低,H2,H3,H4含气量较高,400～2 000 m埋深的褐煤含气量介于2.57～6.99 m3/t之间,且均随埋深增加而增大。含气量中吸附气、水溶气、游离气含量比例分别为78.7%,9.3%,12.0%.     

沁水盆地煤地质与煤层气聚集单元特征研究

通过对沁水盆地煤层气聚集单元分析,可以看出煤层气聚集单元划分需要查明影响煤层气成藏的各种地质因素。煤层气聚集成藏是天然气成藏中的特殊情况,其特殊的成因机制使得聚集单元分析不能套用常规石油天然气聚集单元的划分原则,其中煤地质基础研究特别是煤层气基础研究是煤层气聚集单元分析的基础;对于一个完整盆地,煤聚积规律研究对煤层气最为重要,因此应该在高分辨率层序地层单元划分的基础上进行精细的富煤单元分析;对于指导煤层气勘探与开发,盆地内部次级单元的划分是实用的,也是难度更大的;沁水盆地煤层气聚集单元可以用以下“富气区”描述,即沁南极富气区、东翼斜坡带富气区、西翼斜坡带低富气区、西山较低富气区和高平一晋城低富气区,因此沁南区是煤层气成藏有利区。     

柿庄北深煤层压裂伤害机理及低伤害压裂液评价

我国煤层气地质资源量达36.81×108m3,仅次于俄罗斯和加拿大,其中1 000~2 000 m的煤层气地质资源量占总资源量的61.2%。深煤层煤层气的开发是今后煤层气开发的必然趋势。水力压裂是深煤层煤层气工业开采的主要增产措施。在分析柿庄北深煤层的工程地质特征时发现,深煤层具有低孔隙度、低渗透率、高变质程度和高含气量的特点,在压裂改造时易受工作液体的伤害。因此,针对煤岩主要的伤害类型,对比分析压裂液伤害前后的煤岩电镜扫描结果,研究深煤层煤岩的伤害机理。通过研究得出,相对浅煤层而言,深煤层主要的伤害是吸附伤害和微粒堵塞。最后,根据深煤层岩心的伤害评价方法,在实验室内分别优选出低伤害活性水和泡沫压裂液两种体系,伤害评价结果显示优选的活性水和泡沫压裂液对深煤层的伤害率相对常规压裂液低,可在一定程度上改善煤层气储层压裂效果。     

大倾角储层煤层气多层合采产量控制地质与工程因素

针对大倾角储层煤层气多层合采的特点,以库拜煤田煤层气井的实际排采动态资料为基础,通过分析排采动态典型指标与地质要素和工程要素之间的关系,剖析了库拜煤田大倾角储层多层合采煤层气井产能的控制因素,并用灰色关联分析定量评价了各影响因素的重要性。结果表明：（1）大倾角储层煤层气合层排采产量与单井动用资源丰度、储层压力梯度、煤体结构、临界解吸压力、初始排水速度、压裂效果、初始见气时间具有较好的相关性,但与渗透率、吸附时间相关性较差。储层压力梯度和储层压力是影响该研究区产能的主控因素;（2）新疆库拜煤田大倾角储层靶点压力特征、含气量、渗透率基本处于同一水平,同埋深不同煤层物性非均质性较小,层间干扰作用小,较适合合层排采。论文研究成果可作为大倾角储层煤层气合层排采提供指导。     

沁水盆地南部煤层气藏特征

以油气、煤田和煤层气勘探阶段积累的资料为基础,系统探讨了沁南煤层气藏的特征。通过对气藏静态特征（包括煤层空间几何形态、煤层气成分和含量、储层物性、吸附特征、储层压力及封闭条件）和动态过程（包括煤层气形成、运移和聚集）的分析,指出晚古生代的煤层在经历了印支期和燕山期两次煤化作用生成的煤层气,在喜马拉雅期遭受了严重的调整与改造后逐渐形成现今的沁南煤层气藏。直接控制该煤层气藏中煤层气富集程度的因素为顶底板与边界断层。目前的高产煤层气井基本上都位于地下水滞流区。     

西北地区煤层气藏形成条件剖析

从煤层发育程度、煤相、煤显微组成、煤级、煤变质作用、构造作用、围岩圈闭、地层压力以及水地质条件等方面对西北地区侏罗系及石炭-二叠系煤层气藏形成条件进行了详细剖析。研究结果表明，西北侏罗系及石炭-二叠系在上述条件具备时能够形成煤层气藏。     

Evolution of the CBM reservoir-forming dynamic system with mixed secondary biogenic and thermogenic gases in the Huainan Coalfield,China

The secondary biogenic gas is an important original type of the coalbed methane (CBM) in China. Based on the analyses of sedimentary and burial history of the Permian coal-bearing strata, combined with thermal history and gas generation process of coals, the CBM reservoir-forming dynamic system with mixed secondary biogenic and thermogenic gases in the Huainan Coalfield is subdivided into four evolutionary stages as follows: (i) shallowly-buried peat and early biogenic gas stage; (ii) deeply buried coal seams and thermogenic gas stage; (iii) exhumation of coal-bearing strata and adsorbed gas lost stage; and (iv) re-buried coal-bearing strata and secondary biogenic gas supplement stage. The Huainan CBM reservoir-forming model has the features of the basin-centered gas accumulation. The evolution of the reservoir-forming dynamic system proves that the thermogenic gas is not the main gas source for the Huainan CBM reservoir. Only the secondary biogenic gases as an additional source replenish into the coal bed after basin-uplift, erosional unroofing and subsequent scattering of thermogenic gases. Then this kind of mixed CBM reservoirs can be formed under suitable conditions.     

中煤阶煤层气井排采阶段划分及渗透率变化

煤层渗透率动态变化规律是煤层气开发所面临的重点问题之一。根据无因次产气率划分煤层气井排采阶段,结合等温吸附实验下煤层气的解吸过程确定排采阶段分界点位置。通过物质能量动态平衡理论建立中煤阶煤储层渗透率评价模型,从渗透率变化趋势、主导机制、产能动态等方面,阐释了中煤阶煤层气井不同排采阶段煤储层渗透率动态变化特征与控制机理。结果表明,排采过程中,煤储层绝对渗透率发生“先降低-后回返-再上升”的动态变化。排水阶段水相有效渗透率迅速下降,气相有效渗透率为0。储层压力降低至临界解吸压力后进入产气阶段,气相有效渗透率迅速增加,水相有效渗透率缓慢降低。产气量衰减阶段绝对渗透率开始下降,在滑脱效应影响下,气相有效渗透率仍然保持缓慢上升,水相有效渗透率降低。     

用煤层气作为燃料对节能减排的意义

煤层气与煤炭伴生,是以吸附状态储存于煤层内的非常规天然气,是一种清洁能源。论述了山西省煤层气开采的现状及作为锅炉燃料的特点,分析了山西省煤层气产业化发展的有利条件和开发煤层气的重要意义。     

寺河井田下组煤煤层气开发有利区优选及穿煤柱水平井井位部署

寺河井田在煤炭开采前需要通过地面预抽方式降低瓦斯含量以解决煤炭开采过程中的瓦斯突出等问题。煤矿区地面煤层气开发工程要做到与煤炭的协调开发,煤层气抽采区块的优选及井位的合理部署至关重要。本文利用FLAC3D软件模拟,建立煤层底板采动效应地质模型,开展针对性的研究上组煤采动后下伏岩层应力变化;结合煤矿采掘部署,选取下组煤煤层气开发的主控因素为指标,建立采动区下组煤煤层气开发潜力评价指标体系,采用层次分析法和模糊综合评价相结合的方法,评价煤层气开发的有利区块;以煤层气与煤炭协调开发为前提,确定穿煤柱水平井煤层气开发井位部署的原则,研究水平井设计的关键要素及内容,优化设计15口井位。研究表明：9号煤层和15号煤层都处在3号煤层开采卸压范围内;东五盘区是寺河井田部署下组煤煤层气水平井的优选区,开展的1口煤层气井最高日产气量达到了9 522 m3。     

Influence of overpressure on coalbed methane reservoir in south Qinshui basin

In theory, from the high temperature and pressure during the coal generating gas to the present low temperature and pressure of coalbed methane reservoir, the accumulation of coalbed methane was from oversaturated to undersaturated. The gas content of the coalbed methane reservoir in the south Qinshui basin was 12-35.7 m3/t. According to the isotherm and measured gas content of No. 3 coal, the adsorbed gas content in some wells was highly saturated and oversaturated, which was hard to theoretically understand. In addition, there were no thermogenic and biogenic gases at the late stage in the south Qinshui basin. This article proposed that the overpressure was the main reason for the present high saturation of the coalbed methane reservoir. In early Cretaceous, the coalbed methane reservoir was characterized by overpressure and high saturation caused by gas generation from coal measure source rocks. In late Cretaceous, the coalbed methane reservoir was rapidly uplifted, and with the temperature and pressure decreasing, the pressure condition of adsorbed gas changed from overpressure to normal-under pressure, which resulted in the high saturation and gas content in the present coalbed methane reservoir.     

瓦斯突出地球物理场的介质分布特征

研究了瓦斯突出地球物理场的介质分布特征．从关键层（瓦斯突出煤体） 成因机制及其与宏观地质构造之间的关系探讨了其空间分布特征；应用岩石力学、弹塑性力学理论确定了工作面前方应力墙的位置和宽度．为地球物理方法在瓦斯突出灾害预测中的应用奠定了物理性质基础．     

煤层气藏强化开采各向异性力学性质分析

针对煤层多重孔隙系统空间非连续分布、力学属性各向异性的特点,综合考虑注气强化开采过程中多组份多过程物质运移特征,构建了正交各向异性等效连续煤层流固耦合模型,据此进一步剖析了煤层各向异性力学性质及其对孔渗参数与注采能力的影响。煤层各向异性的力学属性,导致开发过程中储层水平应力与应变的动态变化存在明显的方向性特征,沿力学强度或杨氏模量大的方向变化相对较大,进而带来裂缝宽度、渗透率及其变化的方向性差异,同时致使孔隙度、渗透率以及气体吸附浓度空间分布的非均质性,最终造成与横观各向同性介质不同的煤层气生产与CO2注入预测结果。研究成果对煤层气开发过程中孔渗参数及注采能力的准确预测具有重要意义。